Complex repairs for key road
WFor those rebuilding Christchurch’s Sumner Rd, the ‘‘easiest’’ work ended up causing the most problems, Michael Hayward reports. hen work started on the 2.6 kilometre project, which will reconnect Sumner and Lyttelton via a scenic coastal drive, any issues were expected to come from the Sumner end, where a lot of tricky rockfall mitigation work was needed.
By comparison, the work at the Lyttelton end seemed a straightforward rebuild of the road, as rockfall protection work was completed in 2015. But when contractors cleared the fallen vegetation and debris from the tarmac, they found the damage was more extensive than expected.
Project manager Peter Bawden said the job had been ‘‘kind of turned around’’ since it began: ‘‘This [the Lyttelton end] is really the more difficult part of the road to fix now, just because of the number of retaining walls that are in there, and the number of work sites.’’
Some of these retaining walls will take six months to repair, and the logistics of the repairs prevent all of them being worked on at the same time. There are about 30 retaining walls needing replacement or repair along the length of the project.
The problems are exacerbated by the organic-rich soil and wet, south-facing aspect of the slopes at the Lyttelton end. In places, water running through the soil has caused hollows to appear under the road. Even on a dry day several days after heavy rainfall, the hills above the road weep.
Bawden said the bulk of the retaining work should be finished in September. There are about 60 workers from seven subcontracting companies at a dozen sites along the road. In June, workers put in about 14,000 hours.
He described the work as like repairing a house; ‘‘you can’t restore a 1940s house to 1940 standards’’.
The crucial stretch of road, to be used by oversized vehicles or those carrying dangerous goods to Lyttelton Port, was originally due to open in early-2018, but this was pushed back last October due to the issues at the Lyttelton end.
Christchurch City Council transport planning and delivery manager Lynette Ellis said work was on track for the road to reopen in March.
The first stage of work, ensuring the slopes above the road are safe by removing loose or dangerous rock and putting in rock barriers where needed, is complete. It had started in October 2016. Retaining wall and drainage work has started, with final repairs and surfacing to come.
Ellis said the work was complex and dangerous, but the big issue was not being able to get in and see what contractors were working with until the rock remediation finished. It has meant the designs for some sections have had to be adapted or made up as work went on, and some design work was ongoing.
The cost of the repairs are being split between the council and the NZ Transport Agency, with the latter picking up 83 per cent of the funding. It has been budgeted for $40-60 million, but Ellis said the final cost would be ‘‘towards the lower end of the range’’.
Though extensive work has been done to make the road safe from falling rock, it was always a possibility for any road below a hill. Geotechnical advisor Matt Howard said the work had made the rockfall risk on the road comparable to that on other similar roads in New Zealand.
A 400 metre long rock catch bench running below the bluffs is one of the significant pieces of finished work. It starts 600m from the Sumner end and runs back towards Lyttelton.
Workers finished digging out the 15m wide bench in May, with the 1000 cubic metres of removed rock now making an imposing pile below the Sumner end of the works.
Lyttelton Port of Christchurch chief executive Peter Davie said the link between the port and Christchurch had ‘‘high economic importance’’ for the city and region, and Sumner Rd’s opening was ‘‘keenly awaited’’.
‘‘The delay in constructing the road has meant that the Port has been unable to access its quarry, and this has delayed reclamation work and incurred extra costs in procuring rock for projects and maintenance.’’
‘‘[The Lyttelton end] is really the more difficult part of the road to fix now.’’ Project manager Peter Bawden
Sumner Rd has been closed since the February 2011 earthquake.
It is one of four projects making up the council’s Sumner-Lyttelton Corridor Programme, the others being at Wakefield Ave, Moa Bone Point and Shag Rock Reserve.